gdm/X broken by recent update

[Robert William Hutton <rwh@helms-deep.cable.nu>]

Hi,

Last night's update in unstable has killed my xserver.  I'd normally be
able to work out what's going on, but nothing is showing up in my logs.
The symptoms of the problem are also different than the usual ones:

- The X server starts, I get the grey background, and the cross, which
  is the default X mouse pointer.  I can move the mouse pointer around.
- Then, before the GDM window appears, the server just crashes out.

There are no errors in /var/log/gdm/:?.log, /var/log/XFree86.log, syslog
or messages.

When I run startx, I get the grey background and mouse pointer, and some
apps that are being run because they're in my .xsession.  I also get the
gnome 2.4 splash screen very briefly, before the whole thing just
crashes again.  It seems like it's crashing when it's trying to load my
window manager, but I can't imagine why.

I'm very mystified about this; any suggestions would be appreciated.

In a related note, is it possible to work out which packages were
updated?  That way I could perhaps just roll back to the versions I was
running a couple of days ago.  I use aptitude.

Thanks,

Robert.